“We have made some absolutely wonderful friends and relationships that will endure well beyond our departure,” Caldwell said in a letter revealing his retirement from Army North, also known to many here as the 5th U.S. Army.

A former 82nd Airborne Division commander, he oversaw the dramatic growth of Afghan security forces from 2009 to 2011. Those forces in his tenure went from 190,000 soldiers and police to about 330,000.

Caldwell, a 37-year veteran, also grappled with the now-familiar pattern of “insider attacks” launched by Afghan troops against coalition forces. In the winter of 2010, six GIs were killed by Afghan border police in one incident.

A study later showed that most of the attacks were carried out by “lone wolfs” and weren't systemic.

Caldwell got the idea of joining the Army after his father, who headed the 5th U.S. Army from 1978 to 1980, was assigned to West Point.

The younger Caldwell couldn't be reached Tuesday but said last year in an interview, “I thought, 'Gosh, I want to be like them.'”